i88 TUNGSTEN STEELS TABLE XI Composition of Manganese Steels No. C Si Mn P S I . 0-320 0-311 6-32 . 0-077 0-036 0-585 0-265 9-61 0-086 0-042 3 • • 0-804 0-280 8-70 0-034 0-015 4 • • 1-085 0-241 12-24 0-068 O-OI2 TUNGSTEN STEELS Tungsten steels are very hard and serve specially for making tools, permanent magnets, etc. Their analysis includes estimations of the ordinary elements of steel and also of tungsten. 1. Determination of the Silicon and Tungsten.—When tungsten steel is treated with nitric acid, the silicon present separates as silica and the tungsten as tungstic acid. After weighing, the precipitate is treated with hydrofluoric acid, the loss representing the silica and the remainder the tungstic acid. Procedure. 2-5 grams of the finely powdered sample are treated in a covered dish with nitric acid (D 1-18), the solution being evaporated and the residue ignited to decompose the nitrates and taken up in hydrochloric acid. The liquid is then evaporated to dryness, the silica rendered insoluble at 135°, as under 2, p. 172. The residue is moistened with cone, hydro- chloric acid and then just sufficient hydrochloric acid (D 1-12) added to dissolve the ferric oxide in the hot. The liquid is evaporated to a syrup, allowed to cool, diluted with about double its volume of water acidified with hydrochloric acid and, after a few minutes, filtered by decantation. The precipitate is afterwards introduced on to the filter and washed with water acidified with hydrochloric acid until the liquid passing through no longer gives the reaction for iron with thiocyanate.1 After being dried, the filter and precipitate are incinerated in a platinum crucible and the residue ignited at not too high a temperature (not in the blowpipe flame) and weighed. To eliminate and estimate the silica, the weighed mixture of tungstic acid and silica is treated with a little sulphuric acid and a few c.c. of hydro- fluoric acid and the procedure indicated on p. 171 then followed. The loss of weight gives the silica and this, multiplied by 0-4693 the silicon ; the residue is the tungstic acid, multiplication by 0-7931 giving the tungsten. If the sample contains more than 10-15% °f tungsten, it is difficult to attack with nitric acid and it is then advisable to have recourse to fusion (see later: Ferro-tungsten). 1 A yellow ring of tungstic acid, difficult to remove merely by washing, is often formed in the dish. This may be detached by gentle rubbing with a piece of filter paper moistened with ammonia, the paper being then added to the rest of the precipitate.e water.